Effect of an aqueous 4% titanium tetrafluoride solution on preventing caries in orthodontic patients: a controlled clinical trial

ABSTRACT Introduction: Titanium tetrafluoride (TiF4) is a fluoride compound that, when is applied over enamel, promotes a protection against demineralization through a titanium dioxide (TiO2) acid-resistant coat. Objectives: This study sought to verify the hypothesis that a single application of 4% TiF4 increases the resistance of enamel to dental demineralization in orthodontic patients. Materials and Methods: This controlled clinical trial followed CONSORT guidelines and investigated the prevention of enamel demineralization, fluoride retention, and the presence of a Ti layer after TiF4 application on banded teeth exposed to clinical cariogenic biofilm. Forty premolars were divided into a control group (CG; n = 20) and a test group (TG; n = 20). Teeth from both groups received prophylaxis and orthodontic bands with a cariogenic locus. In the TG, all teeth additionally underwent aqueous 4% TiF4 solution application after prophylaxis before being banded. After one month, teeth from both groups were extracted and prepared to assess the microhardness, fluoride retention, and evaluation of the Ti coating over the enamel surface. All data were analyzed with a paired Student’s t-test (p<0.05). Results: Enamel microhardness and fluoride uptake were higher in TG than in CG, while the Ti layer could be seen over TG teeth that received TiF4 application. Conclusion: Under clinical circumstances, the 4% aqueous TiF4 solution was effective in preventing enamel mineral loss through increasing the enamel resistance to dental demineralization, enhancing its microhardness and fluoride uptake, and forming a Ti coat.


INTRODUCTION
Orthodontic treatment with fixed appliances has been established as an integral part of contemporary orthodontics due to its capacity for precisely planned tooth movements in all three planes of space. 1 However, it is well-known that orthodontic patients are more inclined to develop dental caries as a result of their greater difficulty in maintaining adequate plaque control by tooth-brushing, flossing, and mouth-rinsing with fluorides during years of treatment, 2,3 creating a favorable condition for plaque to rapidly adhere and accumulate. 4,5 As a result, enamel demineralization and gingivitis have come to be regarded as the most prevalent consequences of biofilm formation, affecting 50% to 70% of patients with fixed appliances. 6 Fluorides are used in Dentistry to improve the resistance of human enamel against acid attack 1 . However, most of the success of fluoride therapy is patient-dependent, often requiring consecutive appointments to become effective.
Titanium tetrafluoride (TiF 4 ) began to be researched in 1972 by Mundorff et al. 7 and Shrestha et al. 8 , who described its capacity to cover the tooth surface and ability to promote higher rates of fluoride penetration and retention in the enamel.
The created layer also demonstrates less solubility under cariogenic challenge.
Chevitarese AB, Leite KLF, Dutra PB, Pithon MM, Faria LCM, Ruellas ACO -Effect of an aqueous 4% titanium tetrafluoride solution on preventing caries in orthodontic patients: a controlled clinical trial This Ti-rich coat, formed by titanium dioxide (TiO 2 ), is more resistant than any other fluoride agent, 7 decreasing enamel solubility and enamel porosity, 8 reducing caries formation, and enhancing enamel fluoride concentration. 9 Besides, it cannot be removed from the enamel surface by potassium hydroxide 10 or with hydrogen chloride. 11 According to Buyukyilmaz et al. 10 the presence of this Ti coat could be verified over enamel up to one year after its application.
Although there are many studies evaluating TiF 4 efficacy in caries prevention, 12,13 there are also some doubts regarding its effects in orthodontic patients. As such, this study sought to determine the microhardness and fluoride uptake and to evaluate the Ti coat over enamel after the application of 4% TiF 4 on banded teeth submitted to a high in vivo cariogenic challenge.
The hypothesis that a single application of this compound enhances enamel resistance was also investigated.

TRIAL DESIGN
This non-randomized, controlled, split-mouth and single-blind clinical trial was developed and conducted involving patients of orthodontic clinics at an university in Rio de Janeiro (Brazil) and was approved by the research ethics committee. The patients signed a written consent before their participation on the trial. The experimental 4% TiF 4 solution was formulated by dissolving 3.4 g of TiF 4 (Sigma-Aldrich Co., St. Louis, MO, USA) in 100 mL of deionized distilled water. 13 The pH of the fresh solution was 1.0.

CLINICAL PROCEDURES INTERVENTIONS
All 40 premolars received prophylaxis (with fluoride-free prophylactic paste) and were divided (split-mouth) into two groups containing 20 teeth each: a test group (TG) containing teeth from the first and third quadrants, and a control group (CG) containing teeth from the second and fourth quadrants. This quadrant stratification arrangement was made to avoid any interference regarding which side of the mouth the patient brushes their teeth best.
The CG teeth received prophylaxis and orthodontic bands with a cariogenic locus. The TG teeth, after receiving prophylaxis, also had their buccal surfaces treated by a direct passive application of 4% TiF 4 solution (pH: 1.0) for 60 seconds with a Microbrush ® (KG Sorensen), followed by 60 seconds of water-rinsing and 10 seconds of compressed air-drying. These procedures were completed while avoiding any surface contamination by oral fluids, using cotton rolls and saliva suction. Thereafter, the TG teeth also received orthodontic bands with a cariogenic locus.

CARIOGENIC LOCUS PREPARATION
The orthodontic bands received two cuts on the buccal surface, measuring 2 mm in length and separated 4 mm from each other, to create a retention area for biofilm formation (Fig 1).

LABORATORY PROCEDURES
After one month, all premolars were extracted by one blinded calibrated dentist, avoiding any damage to the premolar crowns, and the teeth were stored in a 0.1% solution of deionized water with thymol crystals (pH 7.0). 15 After this point, the bands were carefully removed and all teeth were washed with deionized water to remove plaque and debris.
After root separation, each crown was mesiodistally cut under irrigation using a diamond disc and only buccal surfaces were prepared for laboratory analysis. Each half was included in epoxy resin except for a window (2 mm × 4 mm) on the buccal surface, which was the same as that exposed on the cariogenic locus.

ENAMEL MICROHARDNESS
Twenty teeth were prepared to be analyzed, by a blinded operator, for microhardness 12   Differences between the control and test groups were statistically evaluated using a Student's t-paired test with a significance 12 Chevitarese AB, Leite KLF, Dutra PB, Pithon MM, Faria LCM, Ruellas ACO -Effect of an aqueous 4% titanium tetrafluoride solution on preventing caries in orthodontic patients: a controlled clinical trial level of 5% (p<0.05). The descriptive analysis was done considering whether or not the Ti coat showed through during microprobe analysis with an energy dispersive spectrometer, and the nature of its formation over human enamel.

PARTICIPANT FLOW
All recruited participants remained at the end of the experiment, totalizing 40 teeth (20 of control group and 20 of test group) (Fig 3). The trial period was 30 days, starting with bands bonding and finishing at teeth extraction.

ENAMEL MICROHARDNESS
The results of microhardness are compiled in Table 1

FLUORIDE UPTAKE
The mean values of fluoride uptake of the TG were higher than those of the CG in all specimens (n=40) of both quadrants ( Table 2).

ENAMEL TI LAYER
The superficial Ti layer was present in 100% of the TG (n=20).
The presence of Ti was established by electromicrography ( Fig 4A) and it was verified that the Ti layer was irregular along the surface (Fig 4B). Ti mapping displayed a Ti peak graph (Fig 5).

A B
In CG samples (n=20), the enamel appeared normal (Fig 6A) or showed demineralization in some areas (Fig 7), and no traces of Ti were detected by any Ti peak graph (Fig 6B).  Microhardness measurement is one possible way of gathering information on the degree of demineralization or remineralization. 21 The Knoop microhardness technique is the most commonly used approach and is a simple way of deriving hardness information on enamel. 21 The adoption of this method, if applied perpendicular to the enamel surface, provides information at different depths of a caries lesion. 21 In this study, the probe was applied as perpendicularly as possible to the enamel surface, right on the cervical area of the first premolar crown. Unfortunately, the premolar surface could not be flattened before the experiment because the teeth were in the patients' mouths at the time, and after their extraction they were already covered by the aforementioned TiO 2 layer.  According to the present findings, the presence of a titanium layer could be noted in 100% of the teeth from the TG, reinforcing the idea that, due to titanium's attraction to the oxygen, TiO 2 is formed before free titanium penetrates into the enamel. 33 This enamel protection was effective for all TG samples, although the titanium layer was not homogeneous, which is expected when considering the enamel porosity and surface irregularity.
According to Buyukyilmaz et al. 10 , the TiO 2 coating could be seen after one year of its application over enamel surface. Besides, if this layer may remain over an occlusal surface for one year, when compared to a surface covered by orthodontic bands, a long-lasting protective effect against enamel surface demineralization will be present.

CONCLUSIONS
After the completion of this clinical controlled trial, it could be concluded that: » Enamel microhardness was higher when enamel was exposed to 4% TiF 4 before orthodontic band bonding, indicating that TiF 4 has a good potential to prevent enamel demineralization.
» Fluoride retention was higher in teeth that received a single application of 4% TiF 4 before orthodontic band placement.
» Formation of a rich coating occurred over the enamel surface after the application of 4% TiF 4 . Although the Ti layer was irregular, it was enough to keep the enamel surface caries-free during the four-week experimental period.